A friend of mine was poking around in my fridge the other day, looking for a beer, when he found something truly awful. Asparagus.

'Peruvian?' said Chris with one of those sniffs which sounds more like an expletive. 'Nice one, Mim.'

Having Peruvian asparagus in your fridge is, I now know, shockingly bad form these days. It's like having ivory on your mantelpiece and crocodile shoes in your closet. It's like wearing a mink tippet or not recycling. So you can stop feeling swell about your red chard and curly kale grown by farmers stamped by the Soil Association. A report just published in the journal Food Policy reveals - and this might come as a surprise to the nation's middle-class organic-box-buying masses - that local food is generally more 'green' than organic food. As any astute shopper will have noticed, 76 per cent of the organic produce sold in supermarkets comes from abroad, flown in from the kind of exotic locations that Vogue uses for fashion shoots. Organic it may be, but environmentally sound it most certainly is not.

To add spice to the argument, the study also found that road miles account for proportionately more environmental damage than air miles. Currently, up to 40 per cent of UK road traffic is involved in producing or transporting food; 28 per cent of all freight on the roads of Britain is agricultural produce, and it's being transported 65 per cent further than it was in the Eighties. If supermarkets - and shoppers - were to buy produce from sources within 12 miles, hidden environmental costs would fall from £2.3 billion a year to under £230 million. It hardly takes a genius to see that eating locally makes sense. It cuts pollution. It minimises packaging. It wins you dinner-party brownie points.

Of course, the success of the idea depends on where your home happens to be. I live in Brighton, with the sea ahead and the Downs at my back. Eating locally would surely be a breeze... I tried it for a week to find out.

Day one

Armed with a wicker trug and the very brilliant Sussex Food Finder - a bible for the county's foodies - I head off to Infinity, Brighton's organic superstore. The first thing you learn as a local shopper is that you're suddenly dependent on what's in season. So I'm faced with an awful lot of radishes, which are quite a culinary challenge. You're also dependent on what a small local supplier has managed to produce and get to the point of sale. It could depend on the weather, or the health of his tractor, or whether his dog has fleas. April, it turns out, is known as 'the hungry gap'. There's not a lot out there. Buying local may give you a greater communion with your environment, but, I soon find, it also gives you a lot less control over supper.

I leave the good co-operative folk at Infinity with something called 'Hungry Gap Kale', plus those tubby radishes, new asparagus (Not Peruvian! But £4.80 for seven spears!) and a bag of salad leaves - all from Hankham Farm out towards Eastbourne. I'm rather pleased with my haul, since studies have shown that modern crop-breeding, accelerated growing, storage methods and long-distance transport lower the nutritional value of food. This little lot should be bursting with vitamins, minerals and a general feeling of well-being. Bill: £14.20

Day two

On the way to the gym, I stop at Park Farm Shop in Falmer. Though much of what's on offer hails from local farms, none of it is labelled as such. Local producers obviously haven't yet caught on to branding their wares to ensnare the wandering green pound. The only way I can ascertain what's from where is to engage the farmer in conversation, and he's not exactly what you'd call garrulous. 'Cucumbers,' he says sagely. 'Leeks.' I buy a sheaf of watercress, some stalks of muddy, crooked rhubarb, a cucumber, a brown paper bag of Cox apples and a dozen eggs.

Much as I'd like to cosy up and talk rhubarb all morning, I decide to do the efficient thing and have my next batch of groceries delivered in a box from Real Food Direct, which delivers veg, meat, fish, pastries and pies to the door - all sourced from the local community. My cache includes a fat bouquet of coriander, some lamb neck fillets raised at Boathouse Farm near Lewes, and a pot of yellow honey from Sussex bees. I have a litre of musky Oakwood Farm apple juice, a selection of High Weald cheeses and a wedge of biodynamic cheddar from Old Plaw Hatch Farm just up the A22.

It's all lovely but I get a hefty bill. And what on earth can I cook for supper? I still have an awful lot of radishes. Bill: £64

Day three

Thank heavens, then, for Kudos Foods. The company produces ready-meals using (as far as possible) local produce. Tonight's feast, again delivered to my door, includes a red onion and goats' cheese quiche using Golden Cross cheese by Kevin and Alison Blunt; chicken with tarragon, featuring a bird that lived in nearby Hassocks; Tuscan-style Sussex lamb, with meat from Gote Farm on the Glyndebourne Estate, and a famous local delicacy - Ripe Tart - from an old recipe resurrected by Kudos. This, I muse while shovelling quiche into my mouth, is the convenience food of the future: no mess, no fuss, no preservatives, and - crucially - no guilt. 'As I see it,' says owner Avril Clarke, 'Our competitors are M&S and the supermarket ranges... but we're contributing to reducing car use by feeding 40 people a night from just one van.' I salute her with a fortifying beaker of Breaky Bottom wine from Peter Hall's beautiful vineyard snuck into a dip in the Downs. All this integrity, and I have barely moved from the sofa. Genius. Bill: £31.80

Day four

Call me an old softie, but there is something very pleasing about plugging into the food culture of your own place. It's a habit we've lost over the years, but today, in the spirit of adventure, I'm off in search of the famous Chanctonbury Ring sausage from nearby Steyning. We also buy a cherry cake, a cube of Flower Marie sheep's cheese, a litre of blackcurrant drinking yoghurt, a dozen free-range eggs and a stout bag of horse manure. Just try making lunch out of that. This, so far, has been my key issue with local sourcing: since you're never quite sure what's out there, you often end up with peculiar combinations.

The way around it, I am discovering, is to shop little and often, in the way that our grandmothers did. Bill: £23.65

Day five

Mind you, once you start to scratch the surface of your local farming economy, it's amazing the breadth of choice you'll unearth.

Unbeknown to me, there are 2,500 active farms in Sussex. One of the best is Middle Farm near Firle, which boasts a pedigree herd of Jersey cows and a bustling farm shop selling apple juice pressed that day, together with jams and hams and herbs harvested from hereabouts; today, I pick up a couple of pints of Pookhill milk and a slab of Buttercup cheese. Elsewhere, should the mood take me, I could get gourds from Uckfield, organic basil from a walled garden in Glynde, chestnut mushrooms from Pulborough, or shitake from Blackboys; if I gauge the season, I could have pears, quince and currants from the orchards of the High Weald. There are, of course, Sussex-breed cattle, and salad leaves courtesy of the county's thriving glasshouse industry; there's thyme, savory, oregano and parsley grown on the Downs just outside Brighton. I can get Desirée potatoes or hedgerow wines sold direct from the farm gate, squid and bass and sole from the fisheries at Shoreham, and Sussex butter shortbread delivered to my door by Kate Bakes.

Owner Kate Munt uses eggs from a farm up the track from the bakery, together with West Sussex butter and whatever fruits are ripe. She has even started to supply a small range of products to Budgens in Sussex, through its new regional sourcing initiative. 'It's great that supermarket chains are beginning to work with small food producers to open up local sourcing to a wider local audience, people who maybe don't shop at farmers' markets or farm shops,' she says. It's great, too, that you can have an apple and hazelnut loaf arrive at your door just in time for tea. Bill: £15

Day six

At last, I am turning south to the sea. It transpires, after a most cursory of investigations, that one of the country's best fish merchants is tucked into the arches on Brighton's beachfront, quite literally a pebble's throw from my office. For a year now, I have bought what little fish we eat from the supermarket. Today, I visit Nigel Sayers, one of Rick Stein's food heroes, and come away with a fresh, wet turbot, which - on Nigel's advice - I'm going to bake with a bed of fennel beneath and a little Sussex honey on the skin. 'This is all fresh into Newhaven this morning,' he says, waving a tattooed forearm over local brill, plaice, gurnard, squid, black bream and bass. 'If you eat what's local when it's in season, it's much cheaper than the supermarkets. A gurnard is £2 at the moment - lovely solid, slightly sweet flesh, great on the barbecue...'

For lunch, I nip next door to see Jack Mills and his wife Linda, for the most perfect sandwich known to human kind: a freshly grilled mackerel fillet, caught yesterday, and stuffed anyhow into a chunk of bread, with a squeeze of lemon juice and a grind of pepper. I think ruefully of my lunchtime dalliances with a Pret sushi box, and experience the bitter taste of shame.

I pull myself together, though, in time for supper at Due South, Brighton's award-winning beachfront restaurant, which prides itself on sourcing locally wherever possible. I order a rabbit kebab (featuring wild rabbits shot on the Downs ), a bass fresh off the boat up the coast at Shoreham, and local spinach served with a dash of garlic and cream; there's local lamb, of course - today, a pan-fried Ditchling lamb's liver with bacon and Savoy cabbage. My salad hails from a council-run allotment up the road, where Hilaire, a fabulous hippie who lives in a shed, raises biodynamic leaves. 'We went up there the other day,' says Due South owner and chef, Rob Shenton, 'and there'd been a frost. No salad.

If the sea has been stormy for a couple of days, we have to write 'sorry, no fish' on the chalkboard outside. That's the problem with small producers who sometimes have difficulty supplying and delivering on time. But, you know, that salad is fantastic. It might be expensive - there are no economies of scale, after all - but it really tastes good.' Along with a glass of Kentish wine called Curious Grape, I couldn't agree more. £73 for two seems like a giveaway. Bill: £13 (not including the meal out)

Day seven

I discover Russell's Sussex Farm Goods Store and Deli in Hove. Embarrassingly, it's about five minutes' walk from home, and this is my first visit. Russell's is a temple to local food - delivered in a no-frills box of a shop on a residential side street. Many of the names and brands are now familiar to me (which I find comforting) - and I buy Sussex-made Montezuma chocolate, a big floppy head of lettuce and a packet of bacon from the Weald Smokery at Flimwell.

'Every time you go out,' says my husband on my return (I notice he is waggling half a cold Chanctonbury sausage in my direction), 'you come back hugging a lettuce. And it always costs you 40 quid.'

'Ah,' I sniff, 'But not only am I cutting down my emissions and funding the local economy, not only does the food taste fresh and good, but I'm also helping to secure the flora and fauna of the Downs...'

A team of ITV reporters found this month that shopping at Tesco can be more expensive than trawling independent shops and markets for the same goods. Rhubarb, for example, was 120 per cent more at Tesco than on a market stall; Gala apples cost 88 per cent more at Tesco than at a market in Fulham, west London. A spokesperson for the supermarket responded thus: 'We have never said that we are the cheapest on the High Street... We are often accused of having an adverse effect on local shops, but they can and do compete with us... And,' she adds, in a voice that suggests she is gazing into my soul, 'you could argue that a centralised distribution network is more efficient and environmentally sound than thousands of car journeys made simply to pick up a local lettuce...' This, indeed, is where my week of eating locally comes unstuck. By rights, I should have clocked up 30 miles on my bike this week, but I've done most of it in the car, listening to Radio 2 with the roof down. To right the wrong, I am now debating the purchase of half a lamb for the freezer, boxed and labelled and very well hung from Gote Farm, which recently started supplying direct to local customers. It's by far the most environmentally sound way of eating meat - one road trip, 29 meals - particularly in these parts, where the Downs support some 50,000 lambs. I don't want to be on first-name terms with my supper, but I'd quite like to know that it lived happily nearby before being turned into chops. Bill £38.75

Total bill £200.40

The verdict

£200 is a heck of a lot - £80 more than I spend on a normal week's groceries. Sure, I indulged in specialities and delicacies, but there is no denying that local sourcing is very likely to become the preserve of those who can afford it. Unless, of course, the supermarkets cotton on to its potential.

If I have learnt anything this week, beyond the sheer wealth of flavour available in my own backyard, it is that everyday shopping choices matter enormously - not just in terms of the nebulous food mile, but in terms of their impact on the lives of those who work so hard and with whom we share space.

That, then, is the challenge. Fraternise your butcher, your baker, your goats'- cheese maker, and acquaint yourself with the local tart. Use your feet or your bicycle - and try not to spend quite as much money as I did.

Oh, and by the way, we ate the ruddy Peruvian asparagus. With Parmesan (from Reggiano), a splash of balsamic (from Modena) and pepper (from Kerala). Shoot me, it was fabulous.